The present invention relates generally to organ perfusion devices and techniques of organ perfusion. In particular, the perfusion devices may simultaneously perfuse more than one organ in an independent manner. The perfusion devices may also perfuse organs at either constant perfusion pressure or constant perfusate flow rate, at the discretion of the operator. Methods are provided for simultaneously perfusing multiple organs, perfusing organs on devices capable of regulating both the flow rate and pressure of a perfusate, and measuring the effect of a stimulus, chemical or otherwise, on organ function.
Maintaining viability of animal organs following removal of the organ from the animal's body (ex vivo viability) or during isolation of the organ from the animal's natural circulation is of great importance for medicine, pharmacology, and physiology. Traditionally, excised solid organs have been maintained through a combination of hypothermia and exposure to nutrient solutions. Hypothermia decreases the metabolic activity of cells within the organ. The decreased metabolic activity lowers the cells' demand for nutrients and oxygen while concurrently suppressing the production of toxic waste products. Exposure to nutrient solutions serves two functions. First, the cells of the isolated organ may be exposed to nutrients and/or oxygen. Second, toxic waste products are removed as the solution is washed over or through the organ.
Devices previously used for maintaining ex vivo organ viability have relied on three methods of nutrient solution exposure. In perfusion, the isolated organ is bathed in a nutrient containing culture medium. While this method is effective for bone marrow or other non-solid organ preservation, perfusion does not optimize solid organ preservation as nutrient supply to the interior of the organ relies on diffusion through the more superficial organ tissue.
Perfusion is a method of administering the nutrient solution through the vascular bed of an organ. The nutrient solution is fed into the arterial side of the organ's vascular system. The solution follows the natural circulatory path of the organ and exits the venous side of the organ's circulation. Superfusion combines both perifusion and perfusion of a single organ.
The devices providing perfusion or superfusion of isolated organs regulate the perfusate flow rate or the perfusion pressure, but not both. Organs perfused by devices regulating only the perfusion pressure typically do not have a constant flow of perfusate to the organ. As the blood vessels in the organ dilate or constrict, either naturally or in response to an external stimulus such as hypothermia, the perfusion pressure changes. The perfusion device adjusts the flow rate of the perfusate so as to maintain a constant pressure. As blood vessels constrict, the perfusate flow rate decreases in order to maintain a constant perfusion pressure. Decreasing perfusate flow can cause hypoxia and injury to the isolated organ. As blood vessels dilate, the perfusate flow rate increases to maintain a constant pressure. Increased perfusate flow can cause electrolyte and free water imbalances resulting in edema and functional alterations. Presently available perfusion devices do not provide a means to control both the pressure or flow rate of perfusate into the isolated organ at the discretion of the operator.
Ex vivo viability is of obvious importance for organ transplants. Because the tissue type of transplanted organs must be compatible with the tissue type of the recipient, available organs must often be transported over long distances for long periods of time to reach a compatible recipient. Also, the demand for transplant organs is greater than the supply, necessitating optimized use of limited resources. Organ viability must be optimized during this waiting period to achieve the most effective results. Devices presently employed for organ transplant and preservation neither monitor the physiological state of the transported organ nor respond to organ changes by altering the preservation conditions under which the organ is being maintained. Thus, preventable organ damage may occur during transport. As more diseases are treated by transplantation, especially with fragile organs, optimizing preservation conditions will assume even greater importance.
Also, ex vivo therapies are being developed for the treatment of various diseases. For example, ex vivo lymphocyte stimulation and activation has been employed for the treatment of AIDS-related diseases. Ex vivo therapy may also provide a means to expose an organ to high doses of a therapeutic modality while protecting other organs from the therapy. Cancer chemotherapy is one such example. Solid tumors, such as hepatomas, do not respond well to doses of chemotherapeutic agents that are tolerable to the bone marrow. Ex vivo treatment of the liver could provide very high drug doses to the tumor while sparing the bone marrow. For effective ex vivo treatment, however, the organ must be perfused so as to optimize viability. Hence, the perfusion device must be capable of delivering adequate levels of perfusate to the organ, monitoring the function and viability of the treated organ, and responding to changes in organ function during treatment. Presently available perfusion devices can not monitor and respond to physiological changes in the isolated organs.
Circulatory isolation of organs within the body is also desirable for medical treatment. If an organ can be perfused in isolation while remaining in the body, many of the advantages of ex vivo therapy may be realized with less morbidity. Catheters that selectively occlude blood vessels leading into and out of a solid organ may be used to selectively perfuse the organ with a therapeutic substance. As in ex vivo therapy, high levels of a drug could be delivered to the diseased organ without risking potentially toxic side-effects in other organs. Also like ex vivo therapy, the perfusion device should be capable of delivering adequate levels of perfusate to the organ, monitoring the function and viability of the treated organ, and responding to changes in organ function during treatment. Otherwise permanent damage to the treated organ could occur.
Isolation of organs from the host circulation, either by organ removal or in vivo circulatory isolation, is also valuable for assessing the pharmacological or toxicological effects of compounds on individual organs. Because a single compound can affect many different organ systems it is often difficult to differentiate the direct effect of the compound on the organ from the effect of the other host responses to the compound. Isolation of the organ from the systemic response of the host provides a means to directly measure the effect of the compound on the organ. Physiological responses to naturally occurring compounds can be similarly assessed. Presently available perfusion devices do not provide the monitoring or perfusate regulating capabilities necessary for assessing complex organ functions or optimizing organ viability.
Measurement of an organ's response to physical stimuli, such as hypothermia, blunt trauma, electrical stimulation, and the like, is also best evaluated by isolating the organ. Similar to measurement of chemical effects on an organ, isolation of the organ eliminates the confounding effects of other host responses. For optimal monitoring, perfusion devices must be capable of altering perfusion characteristics, such as pressure, to differentiate organ effects from vascular effects. For example, hypothermia causes vasoconstriction resulting in hypoperfusion of the organ. Because the delivery of oxygen and other nutrients is altered by the vascular response, the changes in organ function could result from either from cellular effects of the external stimulus or the vascular response to the stimulus. Present perfusion devices do not allow differentiation of these factors.
Devices exist which monitor and adjust the condition of cell culture media. See, e.g., U.S. Pat. Nos. 4,618,586 and 4,629,686. Organ perfusion has special requirements not met by cell culture perfusion devices, however. As noted above, constant pressure perfusion can often result in differences in organ perfusion volume. This difference in perfusate volume can affect the organ's viability and function. A device which provides constant flow perfusion would alleviate this problem. Unfortunately, constant flow perfusion is not always appropriate, such as during extreme vasoconstriction or vasodilation. Comparison to other research often requires constant pressure perfusion also. Hence, it would be preferable for perfusion devices to operate under either constant pressure or constant flow. Perfusion devices available in the art can only perfuse by constant pressure or constant flow.
Physiological or pharmacological research also requires that treated or stimulated organs be compared to control organs. Ideally, the control organ receives identical perfusate at the same temperature, pH, pO.sub.2, pCO.sub.2, etc. Unfortunately, slight variations in perfusate compositions often occur which can alter the normal organ function. Because the baseline functions of the control organ and the test organ are altered by the perfusate differences, it is difficult to accurately interpret test data. A means to deliver perfusate to both organs from the same source would overcome this difficulty and allow for more accurate physiological and pharmacological assessments. Presently available perfusing devices do not fulfill this need.
Even though the test organs and control organs may not be studied under identical conditions, it is necessary to gather both sets of data in modern research. Conducting two sets of tests is time consuming and laborious for laboratory personnel. A device which would study both the test organ and control organ simultaneously would provide a means to increase laboratory productivity and lower the cost of research. In light of the steadily rising cost of research and the increasing scarcity of funding, a means to generate both test data and control data simultaneously is of great importance.
What is needed in the art are perfusion devices which monitor organ function during perfusion, adjust the perfusion conditions to optimize organ viability, provide a means to simultaneously perfuse test organs and control organs with identical perfusate, and are appropriate for in vivo, ex vivo, and in vitro use. Quite surprisingly, the present invention fulfills these and other related needs.